The Presocratic period begins in 585 BC but has no fixed endpoint. It lasts until Socrates changes the focus of the discussion, which must have happened before he was executed by the city of Athens in 399 BC. Some of the Presocratics outlived Socrates. Democritus, for example, seems to have lived until about 370 BC.
The works of the Presocratics have survived only in fragments and second-hand reports. These fragments and second-hand reports are not as a whole (as far as I know) freely available in translation on the internet. (A few of them are available in translation in the Hanover Historical Texts Collection).
Early Greek Philosophy (Eddited and translated by André Laks, Glenn W. Most) in the Loeb Classical Library is available through ASU. This is now the standard source book for the Presocratics. For some information about translations and commentaries, see the list of supplementary texts. For more general discussion, see the Presocratic Philosophy in the Stanford Encyclopedia of Philosophy. (At the bottom of this entry, there is a list of related entries in the SEP.) For additional discussion, see the podcasts at History of Philosophy without any gaps.
The Three Parts of the Presocratic Period
The Presocratic Period divides into three main parts. It begins in the 6th century BC in the city of Miletus (which is on the coast of Asia Minor (modern day Turkey)) with Thales and his fellow Milesian naturalists. Parmenides challenges this new beginning. The Atomists, Democritus and Leucippus, try to bring together the insights of these two prior traditions.
Thales (Θαλῆς), late 7th to middle 6th century
Anaximander (Ἀναξίμανδρος), late 7th to middle 6th century
Anaximenes (Ἀναξιμένης), early to late 6th century
Thales, Anaximander, and the Anaximenes are the Milesian Inquirers into Nature.
Parmenides (Παρμενίδης), late 6th to early 5th century
Democritus (Δημόκριτος), middle 5th to early 4th century
Leucippus (Λεύκιππος), early to late 5th century
Democritus and Leucippus are the ancient Atomists.
Some Historical Events in the World of Ancient Greece
The Mycenaeans were the dominate culture until about the 12th century. Mycenae is a city in in the northeastern Peloponnesus. (The name of the city derives from the poem's of Homer. Agamemnon has his palace and home at Mycenae.) The political organization was an imitation of oriental monarchy. A single monarchical controlled everything. He held a royal domain that contained most of the wealth of the city. He appointed bureaucratic officials to manage this domain and the economy, which consisted primarily in collectivized agriculture and trade.
The Collapse and Breakdown of Civilization
It is this palace economy that collapses completely in about the 12th century. The result is the Dark Ages, in which writing is lost, trade is lost, and civilization breaks down. The Greeks become isolated from the rest of the world. They had to make a new beginning and figure out how to live again. They did this cut off from the great civilizations of Mesopotamia and Egypt.
This resulted in city-states. These city-states were republics. They were not like the cities of the prior Mycenaean Civilization. The differences in wealth among the citizens was small. There were no monarchial rulers who controlled everything. There was no bureaucracy because there was no royal holdings that needed management. There was no caste of priests who controlled religious practice. There were no mercenary soldiers. There was no money to hire them. The citizens themselves had to defend their cities. As independent defenders of their cities, they demanded a role in political decision-making. In this way, the life of the citizen in the "city-state" (πόλις) is political. (The Greek word πόλις transliterates as polis, and it is the etymological root of the English word 'politics.')
People fleeing the collapse of the Mycenaean world moved east to Athens, further east to the islands of the Aegean Sea, and even further to the west coast of Asia Minor. Greeks speaking the Ionic dialect settled in Asia Minor on the coast of the Aegean Sea. This part of the coast came to be called "Ionia," and it was here, particularly in Miletus, the dominant city, that the enlightenment took root.
Trade and Contact with the Great Civilizations
Beginning in about 700, there was a marked increase in trade and colonization throughout the eastern Mediterranean. This brought increasing awareness of the surrounding civilizations of Mesopotamia, Egypt, and, later, Persia. The Greeks, however, were not overwhelmed by these cultures. They assimilated them in a way that would give rise to a philosophical tradition.
Greek and Persian contact came in the form of the Persian Wars, a series of military conflicts between the Achaemenid Empire of Persia and Greek city-states.
By about 550 BC, the Persian Empire had expanded westward. Greek cities on the eastern shore of the Aegean, including Miletus, came under Persian rule. In 492, the Persians invaded in the northern part of the Greek peninsula. In 490, against all odds, the Greeks were victorious against the Persians at Marathon. In 480, the Persians launched a second invasion. Again they were defeated again. This time at sea in the Straits of Salamis.
The Fall of Athens in the Peloponnesian War
In the aftermath of the Persian wars, the Athenians, who played a leading role in winning the war, set up a league of city-states (the Delian League) to clear the Aegean of Persian power. At the same time, the Athenians used funds from the league to rebuild and transform Athens in a way that made it the center of the Greek world. This led to conflict among the members of the league and eventually to the Peloponnesian War in 431. The war would end with Athen's defeat in 404.
The City of Athens executes Socrates in 399 BC
In part because he was blamed for Athen's demise, Socrates was executed in 399. Sometime between his birth in 370 and his execution in 399, he changed the focus of philosophical discussion from the inquiry into nature to matters involving ethics and the good life. This change of focus traditionally marks the end of the Presocratic Period.